1. Field of the Invention
The present invention relates to a composite molding and, in particular, to an improvement in a composite molding that is formed by welding and joining a foam, which comprises a hard skin layer formed by cooling and hardening a foamable synthetic resin by contact with that part of a mold facing a cavity and a foamed layer formed by the foamable synthetic resin in an unhardened state within the skin layer foaming as the pressure of the cavity is decreased, to one surface of a substrate made of a synthetic resin, the surface facing the cavity.
2. Description of the Related Art
A composite molding formed by welding and joining a foam to a substrate is known in, for example, Japanese Patent Application Laid-open No. 6-293039.
When forming a composite molding by welding and joining a foam having a foamed layer within a skin layer to a substrate, as shown in FIG. 9, a cavity 17′ is formed within a mold device, a part of one surface of a substrate 7 facing the cavity 17′, a foamable thermoplastic synthetic resin is injected into the cavity 17′, a hard skin layer 12′ is formed by cooling and solidifying portions of the foamable thermoplastic synthetic resin that are in contact with molds 15′ and 16, and one mold 16 is moved so as to increase the capacity of the cavity 17′ and thereby reduce its pressure, which allows the unhardened synthetic resin within the skin layer 12′ to foam, thus forming a foamed layer 13′ to give a foam 8′ having the foamed layer 13′ within the skin layer 12′. A composite molding 9″ in which the foam 8′ is welded and joined to the surface of the substrate 7 is thus obtained.
During the course of forming the skin layer 12′ by cooling and solidifying a part of the foamable thermoplastic synthetic resin, the cooling rate of the portion of the thermoplastic synthetic resin that is in contact with the substrate 7 is lower than the cooling rate of the portion thereof that is in contact with the mold 15′, and there is therefore a possibility that formation of the skin layer 12′ in the portion that is in contact with the substrate 7 might be inadequate. When forming the foamed layer 13′, the portion on the substrate 7 side that is to form the skin layer 12′ is not hardened adequately, and a foaming gas generated as the unhardened resin foams escapes through the interface between the unhardened portion and the substrate 7 thus raising the possibility that the foamed layer 13′ might not be formed adequately. Furthermore, in a state in which the portion, on the substrate 7 side, that is to form the skin layer 12′ is not hardened adequately, the foam 8′ and the substrate 7 are welded and joined only via the foamed layer 13′, and there is the possibility that the strength of the welding between the foam 8′ and the substrate 7 might be degraded thus causing peel off.